The present invention relates to an image data processor which is employed for processing image data of one page in, for example, a page printer.
Generally, in a page printer, for example, a laser beam printer, it has been so arranged that print data of one page transmitted from a host computer or the like are expanded in a bit map type page memory and scanning by laser beams and an electrophotographic process are started in response to reading of the print data from the page memory such that the image of one page is printed at high speed.
However, since provision of the page memory for one page raises production cost of the memory element, so-called strip map type image processing is usually utilized. In strip map type image processing, an imaginary screen of one page is divided into several to ten plus several bands and two band buffers each corresponding, in capacity, to each of the bands are provided. At the time of printing, the image data are written in and read from the two band buffers alternately such that the image data of one page are outputted to a laser beam generator or the like.
In strip map type image processing referred to above, since the image data are written in and read from the band buffers alternately and continuously a the time of printing, writing of the image data in the band buffers is especially required to be performed at high speed. Therefore, in the known image data processing method, such a problem arises that it is difficult to handle graphic data.
Namely, in the case where data transmitted from a host computer are character data (character codes), it is possible to directly expand (transfer) the data to the band buffers at high speed on the basis of the character codes by referring to character font provided in the printer. Thus, the above described problem can be obviated sufficiently even in the known image data processing method.
However, in the case where data from the host computer are vector type graphic data, it is time-consuming to not only analyze the vector data but obtain dot data through arithmetic operation so as to expand the dot data. Thus, expansion (writing) in the band buffers is performed so belatedly as not to be completed before the next reading and therefore, does not keep up with speed of the electrophotographic process.
Meanwhile, in the case where data from the host computer are raster type graphic data, it becomes necessary to provide a memory area having a large capacity for temporarily storing the graphic data.